Solid! The reason is that solids are more stable than liquids and gases because they have a higher density (more mass per unit volume). This means there's less energy needed to keep them in place compared with other materials like fluids which can easily flow away from their original position when an external force comes into play. Also, since most of us know what "solid" looks/feels like we tend not use it as much for our everyday life so this makes it easier on people who don't understand its properties very well - e.g., kids etc..